Magnetostrictive stress-responsive device and system embodying the same



June 13, 1950 H. c. ROTERS 2,511,178

MAGNETOSTRICTIVE STRESS RESPONSIVE DEVICE AND SYSTEM EMBODYING THE SAMEFiled Feb. 26, 1944 2 Sheets-Sheet l 77 72a FIG.4

as 14 o 0 Q AMPLIFIER o o 5,5 70

INVENTOR ATTORNEY June 13, 1950 H. c. ROTERS MAGNETOSTRICTIVE STRESSRESPONSIVE DEVICE AND SYSTEM EMBODYING THE SAME 2 Sheets-Sheet 2 FiledFeb. 26, 1944 w M 7. 8 o o l l H R A J G E c o F I F m m m L n o B ML mh M v m HAN m 2 l S( A 3 B 3 2 4 M B l wvl w I .m m M M 5 M A 5 a 8 G FFIG. 5

OSCILLOGRAPH MARRA INVENTOR ATTORNEY OSCILLATOR Patented June i3, 195%MAGNE'IOSTRICTIVE STRESS-RESPONSIVE ISJEVICE AND SYSTEM EMBODYING THEHerbert G. Roters, Roslyn, N. Y., assi nor to Fairchild Camera andInstrument Corporation, a

corporation of Delaware Application February 26, 1944, Serial No.524,142

4 Claima (Cl. 73-136) This invention relates to magnetostrictivestress-responsive devices and, more particularly. to such devices of a.type comprising an elongated magnetic member normally circularlymagnetized about its longitudinal axis and subject to longitudinal ortorsional stresses.

It is known in the art that the magnetization of magnetic materials isaccompanied by changes in physical. dimensions and that, conversely,mechanical stresses applied to such magnetized magnetic materials resultin changes in their magnetic characteristics. A wide variety of eflectsmay be obtained dependent, in the case of varying magnetization, uponthe manner in which the materials are magnetized and the manner of suchvariations, and, in the case of varying mechanical stresses upon thetype of stress and its relation to the magnetization; that is, whetherthe stress is transverse, longitudinal, compression, tension, torsion,etc. These various magnetostrictive effects are described generally inthe General Electric Review of March 1942, pages 161-163 and in theappended bibliography.

The present invention is based upon the discovery that themagnetostrictive effects resulting from (1) applying mechanical stressto a circularly magnetized elongated member, known as the inverseWiedeman effect, and its converse (2) applying longitudinal and circularmagnetization to an elongated member to produce a twist, known as theWiedeman effect, are particularly suitable to practical arrangements forindicating, controlling, and measuring various mechanical and electricalquantities. Specifically, in the magnetostrictive phenomenon of thefirst type, the circular magnetization of the magnetic member isdistorted eiiectively into helical magnetization by torsional stresses,resulting in a varying axial magnetization component the magnitude ofwhich may be measured or derived by various means, for example, by awinding surrounding the elongated member in which the variation of theaxial component of magnetization induces an electrical signal which maybe used for measuring, indicating or controlling operation. In themagnetostrictive phenomenon of the second type, the longitudinal andcircular magnetization may be produced in response to fixed or variablequantities and the resulting change in physical dimensions may be causedto represent a variable quantity or the product of two variablequantities.

In magnetostrictive devices of the first type, if the circularmagnetization is maintained con-' stant, the resulting derived effect isresponsive to the rate of change of the applied stress; ii themagnetization is periodic, for example, alternating, the derived effectis responsive to the magnitude of the applied stress; if themagnetization is periodic and it its amplitude is varied pro--portionally with some other variable quantity, for example, velocity,the derived effect is proportional to the product of the stress and thevariable quantity.

Apparatus for indicating, measuring, and controlling operationsembodying the magnetostrictive stress-responsive devices of theinvention have a number of important desirable characteristics andadvantages not found in more conventional apparatus designed forcomparable functions. For example, the magnetostrictive devices of theinvention are efiective to convert force or torque into electromotiveforce without motion and with a high degree of sensitivity, linearresponse. and absence of hysteresis. Due to the fact that the responsecan be effected without mechanical motion, such eflect may be picked upby an inductive coupling thereby avoiding electrical contacts.Furthermore, with such apparatus, an efiect may be derived from theapplication of a steady force in contrast to certain prior art devices,for example, those utilizing piezoelectric crystals, in which an eifectis derived only in response to a rate of change of force.

It is an object of the present invention, therefore, to provide amagnetostrictive stress-responsive device comprising simple and emcientapparatus for measuring, indicating or controlling operations.

It is another object of the invention to provide a magnetostrictivestress-responsive device which embodies one or more of the followingimportant advantages not found in prior art devices designed forcomparable functions: conversion of.

stress into electromotive force without motion; high degree ofsensitivity and linearity of response; absence of hysteresis; derivationof effect by inductive coupling without electrical contacts; andderivation oi effect in response to a steady stress.

In accordance with the invention, a magnetostrictive stress-responsivedevice comprises an elongated magnetic member normally circularlymagnetized about its longitudinal axis and including provisions forapplying to the member a stress to which a response is desired. Thedevice also includes means responsive to the resulting longitudinalmagnetization distortion component of the member, for example, a pick-upwinding surrounding the member, for deriving an effect variable inaccordance with the applied stress.

In a preferred embodiment of the invention, the elongated magneticmember is tubular in form, the pick-up winding surrounds the member andis, in turn, surrounded by shielding means which comprises also a lowreluctance magnetic return circuit for the winding. A utilizationcircuit is connected to the pick-up winding and derives therefrom anelectrical signal variable in accordance with the applied stress.

In accordance with other features of the invention, a magnetostrictivestress-responsive device of the type described is incorporated as a partof various systems for indicating, measuring or controlling variablequantities or conditions, for example, torque, power, fluid, pressure.angular velocity of supporting axes of gyroscopes, electro-acousticalwaves, acceleration, displacement, etc.

As used herein and in the appended claims, the term normally circularlymagnetized member" refers to a member either permanently circularlymagnetized or includingprovisions for applying a magnetizing fieldthereto during normal operation effective to produce circularmagnetization of the member. The term "provisions for applying stress tothe magnetic member is used to denote connections, couplings, flanges,and the like, suitable for connection to external stressdeveloplng orapplying devices but not including such external stress sources.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

I In the drawings, Fig. 1 is an elementary dia gram to aid in theexplanation of the invention; Fig. 2 is a view, partly schematic. of amagnetostrictive stress-responsive device in accordance with theinvention embodied in a power measuring system; Figs. 3A and 3B arecross-sectional and end views, respectively, of a preferred form of themagnetostrictive stress-responsive device of the invention designed toobtain a high degree of sensitivity; Figs. 4, 5,6, 7, 8, and 9 representsystems embodying the magnetostrictive device of the invention forindicating, measuring, responding to, or controlling, respectively,fluid pressure, electro-acoustical waves. acceleration, angular velocityof the supporting axes of a gyroscope, and deflection of a referencebody.

Referring now more particularly to Fig. 1 of the drawings, there isrepresented a magnetostrictive stress-responsive device of elementaryform comprising an elongated magnetic rod member l normally circularlymagnetized about its longitudinal axis. This circular magnetization mayresult from initial permanent magnetization or it may be effected, asillustrated, by passing through the rod longitudinally a current from asource ll, usually an alternating current. The rod 10 is rigidly mountedat one end in a supporting bracket I2 and at the opposite end includesprovisions for applying to the rod a torque stress to which a responseis desired, these provisions comprising a pulley I3 from which issupported a cord l4 and a weight W. The device also includes meansresponsive to the resulting longitudinal magnetization distortioncomponent of the magnetic rod member l0 due to the torque stress appliedby the weight W. This means is illustrated as comprising a pick-upwinding I5 surrounding the rod member .I0 and inductively coupledthereto and provided with terminals B, B, to which there is connected autilization circuit for deriving an electrical signal from the windingI5 variable in accordance with the applied torque stress and comprising,in thi instance, a meter ii.

In considering the operation of the device of Fig. 1, it may be assumedthat initially the weight W is removed and that an alternating currentis supplied from the source II to the circuit A, A

which passes longitudinally through the magnetic rod member It. Thecurrent through the member Ill circularly magnetizes it about itslongitudinal axis but results in no axial magnetization component;therefore, there is induced in the winding I! only a negligibleelectromotive force equivalent to that induced in a single conductorparallel to the member I and of a length equal to that of the windingl-I. It now the weight W is applied as illustrated, the torque stressapplied to the magnetic rod member thereby is efiective to distort thecircular magnetization into a helical magnetization having an axialcomponent. This axial component of alternating magnetization induces inthe winding IS an electromotive force which varies linearly with torqueover a considerable range of torque variation. This electromotive forceis applied to the meter l6 which, by proper calibration, may be made togive a direct indication of the applied torque in any desired unit.

In the systems of Figs. 2 and 4-9, inclusive, of the drawings, themagnetostrictive stress-responsive device represented schematically inFig. l is shown in still more schematic form as the unit M having theterminals A, A for connection to the circuit to effect the circularmagnetization, and the terminals B, B for connection to the utilizationcircuit for deriving a signal from the pick-up winding varying inaccordance with the applied stress.

In Fig. 2 there is represented a system embodying the magnetostrictivedevice of the invention for deriving an effect varying with the poweroutput of a rotating prime mover. This system comprises a prime mover,such as an electric motor 20, connected to drive a load, not shown,through a pulley and belt arrangement 2|, and an axial support for theprime mover consisting of a cradle 22 provided with trunnions 23 and 24.The trunnion 24 is rigidly clamped in a support 25, while the trunnion23 is journalled in a bearing in the support 26. Included as a part of,or a coupling element of, the trunnion 24 is a magnetrostrictive devicerepresented schematically at M and provided with the terminals A, A andB, B corresponding to similarly identified terminals of Fig. 1. Theelongated magnetic member of the device M is circularly magnetized byexciting its winding at the terminals A, A from atachometer 21, drivenby the motor 20, through a high inductance element 28. The eflectresponsive to the resulting longitudinal magnetization distortioncomponent of the member of device M is derived in the form of a firstelectrical signal at the terminals B, B, which is applied to the inputcircuit of a vacuum tube 29, the output circuit of which includes awinding 30 of a meter 3|. Suitable sources of operating potential, suchas the batteries 33 and 34, are provided for the vacuum tube 29. .r-

In considering the operation of the system of Fig. 2, it will be assumedthat the motor 20 is driving a given load. The torque of the motor shaftis transmitted through the cradle 22 to one end of the elongatedmagnetic member of the magnetostrictive device M, the other of which isrigidly clamped in support 25. Any minute angular deflections resultingfrom a deflection of.

the magnetic member of the device M are permitted by rotation of thetrunnion 23 in the bearing of support 26. An electrical signal derivedfrom the winding of the device M and responsive to the resultinglongitudinal magnetization of its magnetic member is applied to theterminals B, B and thence to the input circuit of vacuum tube 29,wherein it is amplified and applied to the winding 30 of meter 3!.Assuming that tachometer 21 develops an output voltage proportional tospeed over the normal speed range of motor 20 but of a frequency varyingwith the speed of the motor, the amplitude of the exciting current ofthe device M is maintained substantially independent of the frequency ormotor speed by the inductor 28 in circuit therewith. At any given speedand frequency, the signal appearing at the terminals B, B isproportional to the longitudinal distortion magnetization component,that is, to the torque of motor 20. However, as the motor speed varies,the frequency of the constant exciting current of device M variescorrespondingly resulting in a variation in the induced voltage in thepick-up winding of device M in accordance with motor speed so that thesignal appearing at terminals B, B is proportional to the product of thetorque of motor 20 and its speed, that is, to its power output. Byproper calibration, the deflection of the meter 3i may be made toindicate directly the power output of the motor 20 in any desired units.

Figs. 3A and 3B are, respectively, longitudinal cross-sectional and endviews of a preferred construction of'the magnetostrictive device of thepresent invention and particularly suitable for embodiment in the systemof Fig. 2. In the construction of Figs. 3A and 3B, the magnetic membercomprises an elongated tubular member 56 on which is disposed'a pick-upwinding 4! comprising a large number of turns and provided withterminals B, B. The winding 4| is formed in a spool 42 ofsuitablein'sulating material which is loosely fitted on the member 40.The member 40 includes provisions for applying thereto a stress to whicha response is desired comprising the clamps 43 and 44 adapted to engageopposite ends thereof and to be connected between two points betweenwhich exists a stress to which a response is desired. For example, theclamp 53 comprises an annulus having a radial slot @311 and a tighteningscrew 43b extending through the slot for tightening the clamp about theend of the member 40. The member 63 is also formed with a series ofscrew-holes 830 by which it may be attached to a suitable couplingmember. The

clamp 44 is similarly constructed except that it is provided with acoaxial hub or sleeve .15 which may be formed integrally with the clamp46 or formed separately and attached thereto by welding, brazing, or thelike. The hub or sleeve 35; may be attached to a coupling element in anysuitable manner. The clamps 43 and Q5 are of nonmagnetic material, suchas brass, while the magnetic member tit is preferably of a highpermeability material, such as a 50-50 nickel-iron alloy hydrogenannealed after fabrication.

The construction of Figs. 3A, 3B also comprises shielding meanssurrounding the pick-up winding Al for minimizing the effect thereon ofextraneous magnetic fields and for reducing the reluctance of themagnetic circuit of the longitudinal magnetization component of themember w. This means comprises the end rings db, a? of high permeabilitymagnetic material disposed with a light press fit on the magnetic memberM at opposite ends of the coil spool 62. The fit should not besumciently tight appreciably to stress the magnetic member 40. Theshielding means also comprises an annular ring 48 of high permeabilitymagnetic material press-fitted over the clamp at and substantiallyenclosing the pick-up winding Bl. In addition, a cup-shaped magneticmember 59 surrounds the entire assembly and is mounted with a press-fiton the clamp 43, being formed with a central aperture 49a looselysurrounding the hub 45 of the clamp 56. It is important in the designand construction of the device of Figs. 3A and 33 to stress magneticmember 40 to a minimum degree and to ensure that any stresses which areapplied to such member are transverse rather than longitudinal and aresymmetrical. This is desirable in order to minimize the zero signalinduced in the pick-up winding M in the absence of an external appliedstress. 7

The construction of Figs. 3A and 33 also includes an electrical circuiteffective when excited to magnetize the member 60 circularly about itslongitudinal axis. This circuit includes the termina'ls A, A andlongitudinal winding 50 threading the tubular member and surroundingsubstantially theentire radial cross section of the magnetic member all..To accommodate the winding an aperture a is formed in the hub 55, whilea slot or keyway will be formed in the coupling element attached to theclamp 43 to accommodate the end portion of the winding 50. A suitableutilization circuit may be connected to the terminals B, B of thewinding M for deriving therefrom an electrical signal variable inaccordance with the torque applied to the member 40.

The operation of the magnetostrictive device of Figs. 3A and 3B is thesame as that described in connection with the device of Fig. 1. Thewinding 50 may be supplied with either direct or alternating current andproduces circular magnetization in the central tubular portion of themagnetic member 60. rent is alternating, a steady alternating voltage isinduced in the winding 4| which is proportional to the product of thetorque on the member 40 and to the exciting current of the winding 50.If the exciting current of the winding 50 is unidirectional, the voltageinduced in the winding 8| is proportional to the rate of change oftorque.

The construction of Figs. 3A and 33 has a number of desirable featuresand advantages, among which may be mentioned the low-reluctance path forthe longitudinal magnetization component of the member 40, resulting inincreased sensitivity; the shielding of the pick-up winding ti from allexternal stray magnetic fields. In addition, the construction of themagnetic member 40 as a tubular element enhances the sensitivity of thedevice, since it concentrates the material of the magnetic member nearthe periphery where it is stressed to the highest degree. Thisconstruction also permits the provision of an exciting winding andcircuit insulated from the magnetic member.

In Fig. 4 there is represented a self-balancing null system embodyingthe magnetostrictive device of the invention for deriving an efiectvarying with the fluid pressure of a fluid system comprising adifierential fluid-responsive device consisting of diaphragm bellows and6| pivotally connected by means of thrust arms 62 and 63, respectively,to a cross link 64 which is rigidly connected to the magnetic member ofthe .magnetostrictive device M. The bellows 60 is provided with an inlet65 for connection to the fluid system to be measured. The systemincludes a fluid pressure generating means, such as a centrifugal pump66, connected to the bellows at If the excitation curto act inopposition to the fluid pressure from the inlet 65. The terminals B, Bof the ma netostrictive device Mnderive a first efiect, such as anelectrical signal, variable in accordance with the differential stressapplied to the magnetic member of the device M. The. system alsoincludes means responsive to such derived effect for controlling thefluid pressure generating means 66 to balance its pressure and that ofthe fluid inlet 65 comprising a vacuum-tube amplifier 61 to the inputcircuit of which the derived signal is applied and the output circuit ofwhich is connected to one phase winding 69 oi! a twophase reversiblemotor 69. The motor '69 is provided with a second winding excited from asuitable source of alternating current II. The source II is alsoconnected to the terminals A for applying an alternating currentexcitation of constant amplitude to the magnetizing winding of thedevice M. The reversible motor 69 is connected to operate an adjustablecontact 12 of an adjustable resistor 13 through suitable reductiongearing 14. The pump 66 is driven by a motor I5 excited from a suitablesupply circuit 16 through the resistor 1-3. The adjustable contact 12may be provided with an extension 12a comprising a pointer co-operatingwith a scale 11 to derive a second efiect, that is, a scale indication,varying with the extent of control of the controlling means.

In the operation of the system of Fig. 4 a variation in the fluidpressure at the inlet 65 produces a torsional stress on themagnetostrictive device M, from which there is derived an electricalsignal varying in sense and magnitude with the applied stress. Thissignal is amplified in the unit 61 and applied to the winding 68 ofmotor 69, causing rotation thereof in a direction to adjust the resistor13 in the proper sense to adjust the speed of the motor so that thefluid pressure developed by the pump 66 is adjusted to the same value asthat at the inlet 65. The system is thus restored to equilibrium and thestress removed from the device M. The pointer 12a indicates the newfluid pressure at the inlet 65 and, by proper calibration of the system,may be made to indicate that pressure directly in any desired unit.

cording or pick-up type embodying the magnetostrictive device of theinvention. In this arrangement the device M is rigidly supported at oneend from the pivoted arm 80, while an acoustical device, such as acutter or pick-up needle 8|, is mounted on the end remote from its pointof support and adapted to co-operate with a sound record 82 supported ona rotating turntable, not shown, beneath the cutter or needle 8|.

In case the device of Fig. 5 is used as a pick-up device, a directcurrent or supersonic alternating current is applied to the terminals A,while the audio-frequency output signal is derived from the terminals B.If terminals A, A are excited by direct current, a signal proportionalto the velocity of the needle is developed at terminals B, B while ifthe terminals are excited by a supersonic alternating current, theoutput signal at terminals B, B is proportional to the displacement ofthe needle. If the arrangement of Fig. 5 is used as a recording cutter,the terminals A may be sirnilarly excited while the audio-frequencyinput signal is applied to the terminals B. The principles of operationare substantially identical to those In Fig. 5 is representedschematically an electro-acoustical translating device, either of therewhen operating as a recorder the Wiedemaneflect is utilized ratherthan the inverse Wiedeman effeet, as in the systems previouslydescribed.

In Fig. 6 is represented a modified form of an electro-acousticaltranslating device embodying the magnetostrictive device of theinvention which may be used either as a loudspeaker or as a microphone.ber is connected directly in the exciting circuit between the terminalsA, A, excitation of which produces the desired circular magnetization.Rigidly mounted on the magnetic member 90 is an acoustical vane 9|.Surrounding the magnetic member 90 are the pick-up windings 92, 92connected in series between the terminals B. Surrounding the windings92, 92 and the vane 9I is a magnetic yoke 93 including a recess or soundchamber 94 in which the vane 9| is closely but freely fitted, the member90 being rigidly supported at both ends in the yoke 93 as indicated. Inthe front wall of the yoke 93 is an aperture 95 which vents the soundchamber at the front of the upper portion of the vane 9|, while in theback wall of the yoke 93 is a second aperture 96 which vents the soundchamber at the rear side of the lower portion of the vane II.

In operation, the structure of Fig. 6 may act as a sound reproducer byapplying the audiofrequency input signal to the terminals B and applyinga, unidirectional or supersonic alternating exciting current to theterminals A, A. Conversely, the apparatus may be utilized as amicrophone by subjecting it to sound waves, similarly exciting thecircuit including the terminals A, A, and deriving the audio-frequencysignal from the terminals B. The operation is essentially similar tothat of the apparatus of Fig. 5.

In Fig. 7 is represented schematically a system embodying themagnetostrictive device of the invention for deriving an effect varyingwith rectilinear acceleration and embodying a magnetostrictive device inaccordance with the invention. This apparatus comprises a mass W rigidlysupported from a longitudinal shaft I00 rigidly clamped at opposite endsin the supports I0 I, I02, the axis of the shaft I00 being disposed in aplane including the center of gravity of the mass W and normal to thedirection of acceleration. The axis of shaft I00 is substantiallydisplaced, preferably below, the center of gravity of the mass W, 7

so that it is in unstable equilibrium. A magnetostrictive device M isincluded in the shaft I00 between the point of support of the mass W andone, or preferably each, of the supports IOI, I02, as illustrated. Asuitable source of exciting current I03 is connected to the terminals A,A in such a way as to excite the magnetizing windings of the devices M,M in series. Similarly, the terminals B, B of the devices M, M areconnected in series opposition and act to derive an effect varying withthe longitudinal magnetization component of the magnetic members of thedevices M, M which, in turn, varies in accordance with the rectilinearacceleration of the mass W normal to the plane including the center. ofgravity of the mass W and the axis of the shaft I00. The derivedefifect, that is, the signal from the terminals B, B, may be applied tothe meter I04 which may be calibrated to indicate directly theacceleration of the mass W in any suitable units.

In operation, the rectilinear acceleration of the mass W is efiective toplace torsional stress on the magnetic members of the magnetostrictivedevices M, M from which the system derives an inof the previouslydescribed systems, except that dication in a manner similar to that ofthe previ- In this case, the magnetic mem ously described systems. Byincluding the netostrictive devices M, M on either side of the supportof the mass W and connecting their respective windings with suchrelative polarities as to produce circular magnetizations in themagnetic members of the device's M, M, in the same direction whenviewing them as a single element and by connecting the terminals B, B ofthe devices M, M, so that the signal voltages due to the applied torsionare cumulative, any errors due to the static transverse stressesdeveloped in the magnetic members of the devices M, M are balanced out.

In Fig. 8 is represented a system embodying the magnetostrictive deviceof the invention for deriving an effect varying with a time-derivativeof the angular displacement of an axis of support of a gyroscope withoutprecession; specifically, the system is efiective to derive efl'ectsvarying with the angular velocities of the two axes of support of agyroscope without precession. The system comprises a conventionalgyroscope IIlI mounted on a spin axis S which is preferably thelongitudinal axis of the vehicle on which the gyroscope is mounted. Thegyroscope H is supported in an inner gimbal ring I I I which, in turn,is supported in an outer gimbal ring II2 about a horizontal axis H in aplane including the spin axis S but normal thereto, while the outergimbal rin is mounted from fixed supports H3, 4 about a vertical axis Vnormal to the axes S and H. Instead of the usual pivot at each of thepoints of support of the gimbal system, there are provided rigidsupports including the magnetostrictive devices M1 and M2 mounted on theaxis H, and the magnetostrictive devices M3 and M4 mounted on the axisV. The magnetostrictive devices MlM4 are provided with exciting circuitterminals A1-A4 and pick-up or output windings B1B4 respectively. Theexciting windings A1 and A2 are excited in parallel from a winding I I5of a suitable source of power, such as a generator I", while theexciting windings A3 and A4 are excited from a winding IIB of thegenerator Ill. The output terminals B1 and B2 of the magnetostrictivedevices M1 and M2, respectively, are connected in series with anindicating device, such as a meter I I8; similarly, the output terminalsB3 and B4 of the magnetostrictive devices M3 and M4, respectively, areconnected to a meter I I9.

In operation of the system of Fig. 8 and considering, for the moment,that the windings H5 and H6 constitute independent sources ofalternating current, it is well known that any angular velocity of thegyroscope system about the horizontal axis H results in a torque on themagnetostrictive devices M3, M4 about the vertical axis V. As a result,the longitudinal magnetization components of the magnetic members of thedevices M3 and M4 induce voltages in their pick-up windings which areapplied to their respective output terminals B3, B4 and are added inseries as applied to the meter I Ill. The meter II9, by propercalibration, may be made to indicate directly a time-derivative of theangular displacement, specifically, the first time-derivative or angularvelocity of the system about the horizontal axis H. Similarly, the meterI I8 may be calibrated to indicate directly the angular velocity of thesystem about the vertical axis V. If the windings H5, and H6 constitutesources of direct current for exciting the magnetostrictive devicesM1-M4, the signals developed at the output terminals B1, B2, B3 and B4are proportional to the second timederivative of the angulardisplacement, that is,

assures the angular acceleration, of the system about its axes H and V,respectively. It is noted that precession of the gyroscope system iscompletely suppressed due to the rigid supports of the system with theresult that it is unnecessary to provide an independent gyro-erectingsystem and at the same time the errors introduced by precession of thegyroscope are avoided.

It now the windings H5 and II 8 of the generator II'I constitutequadrature-phase windings 01 a two-phase generator, so that theexcitation of the magnetostrictive devices M1 and M2 is in quadraturewith that of the devices M3 and M4- it can be shown that the vector sumof the voltages induced in the output circuits of the devices M1 and M2and the devices-M3 and M4 represent the true velocity of turn of thegyroscope system about the vertical, provided that the spin axis 8remains horizontal. This resultant may be applied in series to anadditional indicating meter I20 through an amplifier I2I to indicatedirectly the angular velocity of turn of the system about the vertical.

In Fig. 9 is represented a system embodying the magnetostrictive deviceof the invention for deriving an eilect varying with a deflection of areference body. This system comprises a magnetostrictive device Mforming a part of a shaft I30 rigidly clamped at one end in a supportI3I and Joumalled at the other end in a support I32. At the end of theshaft I30 remote from the support I3I are provisions such as a crankpinI33 for angularly deflecting the magnetic member of the magnetostrictivedevice M about its longitudinal axis in accordance with a force or adeflection which it is desired to measure. The exciting circuit of themagnetostrictive device M is energized from an oscillator I 36 of afrequency which is high compared to any frequency of deflection orchange of force to which it is desired to respond. The output terminalsB, B of the device M are connected to the input circuit of a vacuum-tubeamplifier I35 having an output circult I36 comprising a condenser I37and inductor I38 tuned to the frequency of the oscillator I3 3. Asecondary inductor I39 is coupled to the inductor I38 and is connectedto an oscillograph I through a diode rectifier I M.

It will be apparent that, in the operation of the system of Fig. 9,deflections or forces applied to the crankpin I33 produce a longitudinalmagnetizatlon component in the magnetic member of the magnetostrictivedevice M which is effective to induce a first eflect or signal at theterminals B, B. This signal comprises a high-frequency wave as developedby the oscillator I 36 modulated in accordance with the stress appliedto the magnetostrictive device M from the crankpin I33. The first signalis amplified in the amplifier I35 and converted in the rectifier MI to asecond signal which is applied to the oscillograph MW. This secondsignal comprises the modulation envelope of the first signal appearingat the terminals B, B and thus varies in form and amplitude inaccordance with the deflection or force applied to the crankpin I33.This system has an advantage in comparison with the conventional priorart systems in that it obtains a signal proportional to a deflection ora force, as the case may be, instead of to the time-deri tive of thedeflection or force. As a corollary, the signal output of the system iszero when the stress is zero, which avoids the necessity of a carefulcalibration of. the system.

Thus it is seen that the magnetostrictive device of the invention andthe systems describing above embodying such devices have the importtantadvantageous characteristics mentioned above; that is, they areei'i'ective to convert force or torque into electromotive force withoutmotion and with a high degree of sensitivity, linear response, andabsence of hysteresis. For the highest degree of accuracy the systemsshould be operated at as nearly constant temperature as possible. Inaddition, the magnetostrictive devices should be magnetically shieldedas in the structure of Figs. 3A and 33, while the elongated magneticmember of the magnetostrictive device should be of low-hysteresishigh-permeability material, such as the nickel-iron alloy describedabove.

While there have been described what are at sional stress to which aresponse is desired, a

pick-up winding surrounding said member, shielding means surroundingsaid winding and comprising a. low-reluctance magnetic return circuittherefor, and a utilization circuit connected to said winding andderiving therefrom an electrical signal variable in accordance with saidstress.

2. A magnetostrictive stress-responsive device comprising a tubularmagnetic member of substantial longitudinal dimensions, an excitingwinding threading said member and surrounding the radial cross sectionthereof, provisions for applying to said member a torsional stress towhich a response is desired, an annular recess formed in said member, apick-up winding disposed in said recess, shielding means surroundingsaid winding and comprising a low-reluctance magnetic return circuittherefor, and a utilization circuit connected to said winding andderiving therefrom an electrical signal variable in accordance with saidstress.

3. A system for deriving an efiect varying with the torque output of arotating prime mover comprising, an axial support for said prime moverrigidly constrained at at least one end, a magnetostrictivestress-responsive device including a magnetic member of substantiallongitudinal dimensions included in said support between said primemover and said constrained end, means for normally circularlymagnetizing said member about its longitudinal axis, and meansresponsive to the resulting longitudinal magnetization distortioncomponent of said member for deriving an eflect varying in accordancwith the torque output of said prime mover.

4. A system for deriving an eii'ect varying with the power output of arotating prime mover comprising, an axial support for said prime moverrigidly constrained at at least one end, a magnetostrictivestress-responsive device including a magnetic member of substantiallongitudinal dimensions included in said support between said primemover and said constrained end, means for normally circularlymagnetizing said member about its longitudinal axis, means fordeveloping a first electrical signal variable in accordance with thespeed of said prime mover and for exciting said magnetizing meanstherewith, means responsive to the resulting longitudinal magnetizationdistortion component of said member for deriving a second electricalsignal varying in accordance with the product of torque output and speedof said prime mover, and a power meter responsive jointly to said secondsignal.

HERBERT C. ROTERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 302,976 Brackett Aug. 5, 18841,821,836 Hull Sept. 1, 1931 1,831,597 Henderson Nov. 10, 1931 1,882,401Pierce Oct. 11, 1932 2,053,560 Janovsky Sept. 8, 1936 2,180,176 StoneNov. 14, 1939 2,193,707 Baumann Mar. 12, 1940 2,269,068 Corbin Jan. 6,1942 2,287,794 Gunn June 30, 1942 2,338,732 Nocker Jan. 11, 19442,365,073 Haight Dec. 12, 1944 2,385,005 Langer Sept. 18, 1945 FOREIGNPATENTS Number Country Date 49,262 France Nov. 12, 1938 442,441 GreatBritain Feb. 3, 1936 659,658 France Feb. 5, 1929 831,342 France June 7,1938 OTHER REFERENCES An article entitled, "Application of the inverseWiedemann efiect to torque measurements and to torque variationrecordings," by Tatuo Kobayasi. Article 52 of Reports AeronauticalInstitute of Tokio University. Pa8es425 to 445.

